Method of making beryllium fluoride



Patented Oct. 16,1945

amn

No Drawing. Application April 24,1943, Serial No. 484,477

METHOD OF FLU 17 Claims.

This invention relates to the production of beryllium fluoride-which isa compound usable as a source of metallic beryllium as well as for otherpurposes. One object of the invention is to provide simple andeconomical methods by which beryllium may be extracted in the form of afluoride from siliceous beryllium ores such as, for example, the mineralberyl. Beryl is a berylliumaluminum silicate generally described by theformll18. BeaA12(SieO1a). It can be considered, for practical purposes,as being composed of the oxides of beryllium, aluminum and silicon.Theoretically it contains about per cent by weight of beryllium,although, as mined, it often contains as little as 3.5 per cent of thatmetal. Another object of the invention is the provision of methods bywhich beryllium oxide, or materials or mixtures containing the same, maybe treated to form beryllium fluoride. A further object is to providemethods by which these objects may be achieved by treatment which do notinvolve the use of chemical solutions.

The invention comprises a process in which the material which affords asource of beryllium is mixed with aluminum fluoride and the mixtureheated to cause reaction between the components thereof and theevolution therefrom of a Vapor containing beryllium, which vapor maythenbe condensed'and the condensate used or, if desirable or necessary,further treated to recover beryllium fluoride in substantially pureform. We have found that the temperatures necessary to promote thereaction in such a mixture are low, particularly when reduced pressuresare used, and thus compatible with commercial operating conditions andavailable equipment. We have further found that the presence ofmagnesium fluoride will promote the efficiency and speed of thereaction. We .have also found other conditions which will promote andexpedite the recovery of beryllium fluoride, all of which areparticularly described and explained in the following specificdescription of the methods of this invention.

When beryl, or other siliceous ore of beryllium, is the substance to betreated, it is first desirable to eliminate therefrom all or a greaterpart of the silica prior to the treatment with aluminum fluoride.Otherwise there will be preferentially formed, when the ore-aluminumfluoride mixture is heated, quantities of volatile silicon fluoridewhich will pass ofi as a vapor and thus impoverish the reaction mixtureof fluoride available for forming beryllium fluoride. To eliminate thesilica may not, within the sense of this invention,

mean the physical removal of the silica from the ore or the reactionmixture, although this may, if desired, be effected; rather it meansthat the silica is either removed or converted in situ to silicon or toa silicon compound which does not readily react with aluminum fluoridein the heating of the mixture of aluminum fluoride and source ofberyllium or otherwise render ineffective the fluorine of the aluminumfluoride. The step of eliminating the silica. from the ore may thereforeconsist of any one of several treatments which will either reduce thesilica to metallic silicon or will change the silica to a compound whichis stable, as regards aluminum fluoride, at the temperatures of theproposed reaction. While there are several of such treatments, we preferthe following which have given good results and are also indicative ofmethods by which the silica may be eliminated from the ore.

(a) The beryl, first ground to a finely divided form, is mixed withsumcient carbon to reduce its predetermined silica content to metallicsilicon. Iron is also added to the mixture. The mixture is then heatedathigh temperature, such as 1900 C. or higher, with the result that thesilica is reduced to metallic silicon which then alloys with the iron toform ferro-silicon which is tapped off, leaving a molten slagsubstantially free of silica and composed of the oxides of beryllium andaluminum.

(b) The same mixture as is described above is heated at a temperaturehigh enough to cause the silica to be reduced and permit the silicon toalloy with the iron to form ferro-silicon, but not high enough to meltthe oxides of beryllium and aluminum. For example, a temperature ofabout 1300 C. or higher may be used satisfactorily. The ferro-siliconformed is not separated from the rest of the charge.

(c) The beryl is mixed with sufllcient carbon to reduce the silicaaccording to the reaction sent the fluosilicate R'zSiFo where R. equalsthe alkali metal. This mixture is then heated to effeet the reaction toform said fluosilicate. This step may be conveniently practiced asa partof the beryllium fluoride-producing reaction, in which case aluminumfluoride is also added as described below; the alkali metal fluoride andthe aluminum fluoride may also be introduced into the mixture, at leastin part, by the use of a double fluoride of aluminum and alkali metalsuch as, for instance, cryolite or chiolite.

In process (a) above described the unwanted silica.is actually removedfrom the beryl. In processes (b), (c), and (d) the silicon values of thesilica remain with the other components of the beryl, but the silica ischanged to a materialferro-silicon in one case, probably silicon carbidein another, and alkali metal fluosilicatein the other-which is notnoticeably reactive with the aluminum fluoride in the heating operationfor producing beryllium fluoride. In all processes the silica. has been,in the sense of this invention, eliminated from the siliceous berylliumore.

It will be evident that whenever the siliceous ore is so treated thereremains, apart from any silicon compound, the oxides of beryllium andaluminum. These are now, in accordance with the principles of thisinvention, mixed with aluminum fluoride and the mixture heated toproduce beryllium fluoride in vapor form. For this purpose the reactantsare reduced to a finely divided formpreferably 100 mesh size orsmaller-and thoroughly mixed. If preferred, this mixture may then bebriquetted to prevent dusting and to achieve more intimate contact ofthe components thereof, or it may be used in non-compacted form. If thebonding material used in making the briquettes contains volatilematerials, these should preferably be driven oil by a preliminaryheating at less than reaction temperatures.

The proportioning of the reactants is of some consequence. For eflicientoperation the aluminum fluoride should be present in amounts of at leasttwo molecules thereof for every three molecules of beryllium oxide.However, some of the aluminum fluoride may volatilize as such in theprocess, and additional fluorine values may be lost if residual silicaor other material with which aluminum fluoride reacts in the process,other than beryllium oxide, is present in the reaction mixture.Consequently, it is desirable to furnish sufficient aluminum fluoride inthe reaction mixture to provide an aluminum fluoride-beryllium oxidemolecular ratio of 2:3 in addition to such aluminum fluoride asvolatilizes or takes part in side reactions, in order to insure that thehighest possible yield of beryllium fluoride is obtained. The bestmanner in which to ascertain the excess necessary for maximum results isto make a trial test of the method and analyze the sublimate obtained bycondensing the vapor, as well as the residue of the reaction, todetermine the distribution of the fluorine during reaction.

The reaction mixture thus formed is then heated. If the heating takesplac at atmospheric pressures, the temperature should be maintained atat least 1000 C., and for best results a temperature of at least 1200 C.is preferred. By conducting the reaction at reduced pressures somewhatlower temperatures can be employed without lowering the speed andefliciency of the to the reaction and thus effecting conversion of thesilica to RaSiF'a and production of beryllium fluoride at the same time,the minimum temperatures to be employed are slightly higher than abovestated. Thus, when the reaction is at atmospheric pressure a temperatureof at least 1100 C. should be used, and when the reaction is at reducedpressure a temperature of at least 900 C. should be used.

At these temperatures the reaction proceeds to the production ofberyllium fluoride in vapor form and the vapor is drawn or led from thereaction mass to a relatively cool condensing surface where it iscondensed and thus recovered. The condensate may contain othersubstances, notably aluminum fluoride, and also alkali metal fluoride insome quantity where one of the reactants is an alkali metal fluoride, aswell as other impuri ties. If desired, these additional substances maybe removed from the beryllium fluoride by fractional distillation andcondensation.

It will be noted that in the complete process of treating the beryl orother siliceous ore to obtain beryllium fluoride, it is often possibleto combine the step of eliminating the silica content of the ore withthe step of converting the beryllium content of the ore to berylliumfluoride in vapor form. This is particularly true where an alkalifluoride is used as the eliminating agent, and is also true where carbonis used to convert the silica to silicon carbide.

When an ore of beryllium which does not contain substantial amounts ofaluminum is to be used as the source of beryllium-for example, whenberyllium oxide is used as the source of beryllium-it will be found thatthe addition to the reaction mixture of alumina or magnesia willincrease the efllciency of the reaction, at least in the sense ofgreater yields per unit time. The exact action of these materials is notentirely understood, but they are apparently inert during the reactionand do not appear to enter into it. When present in an amount as low as10 per cent of the reaction mixture, their effect is noticeable, and theamount of alumina or magnesia which will give best results may be easilydetermined by trial under the operating conditions above noted.

We have further found that magnesium fluoride will, when present in thereaction mixture, materially increase the yield of the berylliumfluoride obtained in a given time by the practice of the methods of thisinvention. This is true even when the magnesium fluoride added replacesa part of the aluminum fluoride and thus does not increase the fluorineavailable to the reaction.

In conducting the methods above described for the production ofberyllium fluoride, we prefer to volatilize the fluoride in anatmosphere inert thereto. When the reaction takes place at lowpressures, the presence of a partial vacuum usually produces the desiredresult, but when the heating is carried out at atmospheric pressures weprefer to supply an inert atmosphere in contact with the reactionmixture such as, for instance, a hydrogen or producer gas atmosphere,substantially free from moisture.

Set forth below are specific examples of the production of berylliumfluoride in accordance with the principles of this invention:

Example I Finely ground beryl and carbon were mixed thoroughly in theproportions of 72 parts by weight of beryl and 28 parts by weight ofcarbon, and briquetted under pressure. The briquettes were then heatedat 1600 C., to convert the silica-of the beryl to .silicon carbide. Thebriquettes and aluminum fluoride were ground together to 100 mesh sizeor finer, the mix consisting of 140 parts by weight of thecarbon-reduced beryl, and 60 parts by weight of aluminum fluoride. Themixture was then placed in one end of aclosed horizontal retort throughwhich a flow of gas could be maintained, and heated at 1200 C. for 4hours at atmospheric pressure,

Example 11 Beryl was treated to eliminate silica therefrom by mixingtherewith carbon in amount sufficient to reduce the silica, and alsomixing therewith iron. The mixture was heated at about 2000 C. and theresultant ferro-silicon separated from the remaining slag. This slag,which contained about 37 per cent by weight of beryllium oxide, thebalance being aluminum oxide, was then mixed with aluminum fluoride andmagnesium fluoride in the following approximate proportions: slag 49 percent by weight, aluminum fluoride 24 per cent by weight, magnesiumfluoride 27 per cent by weight. All ingredients of the mixture were of100 mesh size or smaller. The mixture was briquetted and the briquettesplaced in a closed horizontal retort. There they were heated for 1 hourat 900 C. at atmospheric pressure after which the pressure was reducedto 2 mm. of mercury and the temperature raised to 1200 C. After 4 hoursat this temperature 88 per cent of the beryllium content of the reactionmixture had vaporized and had been condensed as beryllium fluoride. Thecondensate contained about 83 per cent of beryllium fluoride, thebalance being largely comprised of aluminum flueride and magnesiumfluoride.

E sample I I I Aluminum fluoride and beryllium oxide, ground to at least100 mesh size, were mixed thoroughly in the proportions of 45 parts byweight of beryllium oxide and 105 parts by weight of aluminum fluoride,and the mixture was briquetted under pressure in a mold. The briquetteswere placed in one end of a closed, horizontal retort having a vacuumpump attached to the opposite end and were heated at 1000 C. for 1 hour,after which the heating was continued for 4 hours while the residual gaspressure in the retort was maintained at 24 mm. of mercury by means ofthe vacuum pump. The portion of the furnace adjacent the end to whichthe vacuum pump was attached remained cool enough to condense the vaporsproduced from the briquettes. Upon being opened, the retort containedsublimate composed of '77 per cent of beryllium fluoride and 18 per centaluminum fluoride, and the beryllium fluoride represented '70 per centof the beryllium present in the orisinal mix.

Divisional applications of the present case and our copending case484,476, claiming related subject matter, have been filed as SerialNumbers 578,940, 578,941, and 578,943.

We claim:

1. The method or recovering beryllium values in ,the form of berylliumfluoride from siliceous beryllium ores which comprises treating the oreto eliminate silica therefrom, mixing the treated ore with aluminumfluoride, heating said mixture at a temperature above 700 C., andcondensing the resultant vapor.

2. The method of recovering beryllium values in the form of berylliumfluoride from siliceous beryllium ores which comprises treating the oreto eliminate silica therefrom, mixingthe treated ore with aluminumfluoride and magnesium fluoride, heating said mixture at a temperatureof at least 1000 0., and condensing the resultant vapor.

3. The method of recovering beryllium values in the form of berylliumfluoride from siliceous beryllium ores which comprises treating the oreto eliminate silica therefrom, mixing thetreated ore with aluminumfluoride, heating said mixture at a temperature of at least 1000 C., andcondensing the resultant vapor.

4. The method of recovering beryllium values in the form of berylliumfluoride from siliceous beryllium ores which comprises treating the oreto eliminate silica therefrom, mixing the treated ore with aluminumfluoride, heating said mixture at a temperature of at least 1200 C. atatmospheric pressure, and condensing the resultant vapor.

5. The method of recovering beryllium values in the form of berylliumfluoride from siliceous beryllium ores which comprises treating the oreto eliminate silica therefrom, mixing the treated ore with aluminumfluoride and magnesium fluoride, heating said mixture at a temperatureof at least 1200 C. at atmospheric pressure, and

condensing the resultant vapor.

6. The method of treating siliceous beryllium ore to recover berylliumfluoride therefrom which comprises forming a mixture of ore, iron, and

sumcient carbon to reduce at least partof the silica of said ore,heating said mixture at a temperature sumcient to cause the saidreduction of silica to take place, mixing the resultant product withaluminum fluoride, heating said mixture at a temperature of at least 7000., and condensing the resultant vapor.

'1. The method of treating siliceous beryllium ore to recover berylliumfluoride thereform which comprises forming a mixture of ore, iron, andsuflicient carbon to reduce at least part of the silica of said ore tometallic silicon, heating said- I mixture at a temperature of at least1900 C.. removing the ferro-silicon thus formed, mixing the residue withaluminum fluoride, heating aid mixture at a temperature of at least 1000C., and condensing the resultant vapor.

8. The method of treating siliceous beryllium ore to recover berylliumfluoride therefrom which comprises mixing the ore with sufflcient carbonto convert at least a part of the silica content thereof, efiecting saidconversion by heating said mixture at temperatures between about 1500 C.and 1800 C., mixing the resultant product with aluminum fluoride,heating said mixture at a temperature of at least 1000 C., andcondensing the resultant vapor.

9. The method. of treating siliceous beryllium ore to recover berylliumfluoride therefrom which comprises mixing the orewith sufllcient alkalimetal fluoride to convert at least part of the silica content thereof toalkali metal fluosilicate, heatin: the mixture to. effect suchconversion, mixing the resultant ore-fluosilicate mass with aluminumfluoride, heating said mixture at a temperature or at least 1000 0., andcondensing the resultant vapor.

10. The method treating siliceous beryllium ore to recover berylliumfluoride therefrom which comprises mixing the ore with suflicient carbonto convert at least part 01 the silica content there- 01, eflecting saidconversion by heating said mixture at temperatures between about 1500 C.and 1800 C., mixing the resultant product with aluminum fluoride andmagnesium fluoride, heating said mixture at a temperature of at least1000" 0., and condensing the resultant vapor.

11. The method or making beryllium fluoride which comprises forming amixture containing beryllium oxide and aluminum fluoride, heating saidmixture at a temperature of at least 700 0., and condensing theresultant vapor.

12. The method of making beryllium fluoride which comprises forming asubstantially silicairee mixture containing beryllium oxide and aluminumfluoride, heating said mixture at a temperature of at least 700 C., andcondensing the resultant vapor.

13. The method of making beryllium fluoride which comprises forming asubstantially silica tree mixture containing beryllium oxide, aidminumfluoride and magnesium fluoride, heatin: said-mixture at a temperatureor at least 700 0., and condensing the resultant vapor.

14. The method or making beryllium fluoride which comprises rorming amixture or beryllium oxide, aluminum oxide and aluminum fluoride,heating said mixture at a temperature or at least 100 C., and condensingthe resultant vapors.

15. The method of making beryllium fluoride which comprises forming asubstantially silicairee mixture or beryllium oxide, aluminum oxide andaluminum fluoride, heating said mixture at a temperature oi at least 7000., and condensing the resultant vapors. I

16. The method of making beryllium fluoride which comprises forming asubstantially silicafree mixture of beryllium oxide, magnesium oxideCHARLES B. WIIIEMORE. FRANK D. CHEW.

